1. Field of the Invention
The present invention relates to an electroluminescence (hereinafter simply referred to as “EL”) panel having an EL element in each pixel, and in particular to an EL panel having a micro-resonator (microcavity) in each pixel for intensifying light of a particular wavelength.
2. Description of the Related Art
Recently, flat panel displays (FPD) having thin thickness and a size which can be reduced have attracted much attention. A liquid crystal display device which is a well known example of the FPD is already used in various devices. In addition, much research and development are dedicated to light emitting devices (such as a display device and a light source) which use a self-emissive EL element, and in particular, to organic EL display devices (organic EL panels) which can emit light with various emission colors and at a high luminance depending on the material of the organic compound(s) to be used.
Unlike a method employed in the liquid crystal display devices in which a liquid crystal panel which is provided in front of a backlight as a light valve controls transmittance of light from the backlight, because the organic EL display devices are self-emissive, the organic EL display devices fundamentally have a high usage efficiency of light, that is, a high output efficiency of light to the outside, and thus, the organic EL display devices allow for light emission of high brightness.
In the organic EL element, however, an organic layer is degraded with use, and in particular, there is a problem in that when the current to be applied through the organic layer is increased in order to increase the light emission luminance, degradation of the organic layer is accelerated.
In consideration of this, methods are proposed in which an intensity of light of a particular wavelength is strengthened using a micro-resonator (microcavity) in an EL display device as disclosed in, for example, Japanese Patent Laid-Open Publication No. Hei 6-275381 and Takahiro NAKAYAMA and Atsushi TSUNODA, “Element with a Light Resonator Structure”, Japan Society of Applied Physics, Organic Molecular Electronics and Bioelectronics division, Third Convention, 1993, p. 135-p. 143.
When a microcavity is used, however, there is a problem in that a dependence of the display color on the viewing angle (viewing angle dependency) is increased. Specifically, because an optical length of the microcavity when the microcavity is seen from the vertical direction differs from an optical length of the microcavity when the microcavity is seen from a tilted direction, the wavelength of light intensified by the microcavity will differ depending on the angle of view.
Thus, there is a demand to alleviate the viewing angle dependency when a microcavity is used.